Parallax scrolling

[citation needed] Some display systems support multiple background layers that can be scrolled independently in horizontal and vertical directions and composited on one another, simulating a multiplane camera.

On such a display system, a game can produce parallax by simply changing each layer's position by a different amount in the same direction.

Programmers may also make pseudo-layers of sprites—individually controllable moving objects drawn by hardware on top of or behind the layers—if they are available on the display system.

The Amiga computer has sprites which can have any height and can be set horizontal with the copper co-processor, which makes them ideal for this purpose.

Risky Woods on the Amiga uses sprites multiplexed with the copper to create an entire fullscreen parallax background layer[9] as an alternative to the system's dual playfield mode.

The more sophisticated games on such systems generally divide the layer into horizontal strips, each with a different position and rate of scrolling.

The program will then wait for horizontal blank and change the layer's scroll position just before the display system begins to draw each scanline.

Some platforms (such as the Commodore 64, Amiga, Master System,[10] PC Engine/TurboGrafx-16,[11] Sega Mega Drive/Genesis, Super NES, Game Boy, Game Boy Advance and Nintendo DS) provide a horizontal blank interrupt for automatically setting the registers independently of the rest of the program.

If each scanline has its own layer, the Pole Position effect is produced, which creates a pseudo-3D road (or a pseudo-3D ball court as in NBA Jam) on a 2D system.

[24] A undated study occurring during or after 2010 by Dede Frederick, James Mohler, Mihaela Vorvoreanu, and Ronald Glotzbach noted that parallax scrolling "may cause certain people to experience nausea.